Determination of the organization of proteins and lipids within biological membranes underlies our ability to understand the functions of cell membranes and the cell itself. Such basic knowledge is important to an understanding of any disease at the cellular and molecular level. We will concentrate upon the existence and functional role of associations between membrane proteins. The Ca++ ATPase, the Ca++ pump of mammalian muscle, and bacteriorhodopsin, the bacterial light activated H+ pump, are the two proteins to be studied. In these studies we will further develop and apply new and powerful fluorescence quenching and energy transfer techniques to measurement of the state of self-association of these proteins. We will try to identify the environmental factors which may promote or inhibit oligomer formation, with special emphasis on the role of different phospholipids and cholesterol. By correlation of enzymatic activity and oligomeric state we hope to determine whether oligomers are required for or regulate biological function. Our long term goal is to develop the fluorescence techniques we will use for more general and routine applications. Eventually, we would like to examine the role of membrane receptor aggregation in hormone function and internalization.